1. Field of the Invention
The present invention relates to a traveling crane having a jib derrickably attached at an end of a boom and an assembling method thereof.
2. Description of the Related Art
For transportation to a work site, a large scale traveling crane is divided into a crane body, attachments, such as a boom and a jib, and components of derricking (raising and lowering) devices for the attachments, so that these divisions are assembled on the work site.
Among lower and upper spreaders around which a jib derricking rope is routed, the upper spreader is necessary to be drawn and to be pulled back during disassembling; since the upper spreader is heavy to be moved by man power, the drawing and pulling back during disassembling of the upper spreader are performed using a hoisting force of a winch.
For example, a technique disclosed in Japanese Unexamined Patent Application Publication No. 11-292471 using a hook-hoisting (a hook winding-up) winch as an auxiliary winch has been known.
This method is that a pulling rope drawn from a auxiliary winch dedicated for assembling/disassembling is fixed to an upper spreader, and by rewinding a jib derricking rope while winding this pulling rope, the upper spreader is moved along an upper boom surface horizontally from a boom anchor (one end of the boom close to the crane body as a base machine) toward a far end of the boom (the other end of the boom connected to the jib).
In this method, there has been a problem that a dedicated guide sheave for assembling/disassembling must be provided at an end of a rear member constituting a strut for moving the upper spreader, so that the weight in the vicinity of the boom end (around the strut) becomes larger, having disadvantages in operating efficiency and in cost overrunning due to the additional sheave.
On the other hand, when the jib derricking rope is rewound (being wound during disassembling) while the hook-hoisting rope is wound (being rewound during disassembling), since the synchronization of both the ropes depends on manual operation of an operator, there have been problems due to asynchrony that both the ropes may tear off or a physical facility may break due to excessive tension thereof, or in contrast irregular winding is caused by excessively small tension of the rope.
In addition, in the technique of the Publication, the asynchrony may be absorbed by the rotational displacement of the strut; however, this only is insufficient for maintaining the proper rope tension because the rotational displacement of the strut is limited by a backstop. Also, in this technique, the upper spreader is floated and moved toward the end of the boom, and then, the spreader is descended along the upper surface of the boom by rewinding the hook-hoisting rope so as to connect the spreader to a guyline of the strut. During disassembling, the upper spreader is moved toward the boom anchor through the reverse procedure thereto.
However, in this method, when the upper spreader is moved along the boom upper surface horizontally, the spreader may interfere with members located on the boom upper surface, such as ropes and piping (referred to obstacles below), so that not only the movement of the spreader is hindered but also both components may be damaged.
On the other hand, in the floating system floating the upper spreader in the air, although this interference can be avoided, since the heavy upper spreader with a weight of 300 kg or more has to be floated and moved, the winch must be carefully operated, so that operating efficiency is reduced lower than in the horizontal movement system.